On a non-root bridge, the root port is the port that receives the best BPDU toward the root bridge.
STP selects the root port by comparing several parameters in order. The first important parameter is the root path cost (RPC), so option B is correct. If multiple ports have the same RPC, the switch then compares the bridge ID (BID) of the upstream device sending the BPDU, making option C correct. If those are still equal, the switch compares the port ID (PID) of the upstream sending port, so option D is also correct.
If all of those values remain identical from the switch's perspective, the device can finally compare the local port ID to determine which local interface becomes the root port, so option A is also correct. HCIA-Datacom teaches this comparison logic as part of STP election rules. The process ensures deterministic selection of a single root port on every non-root switch.
Understanding the comparison sequence is essential for predicting STP topology behavior and for influencing port roles through path cost tuning or bridge-priority adjustments during campus network design and troubleshooting.